The first miniature pressure transducer was described by Collins in 1967 for a bio-medical application. See Collins, "Miniature Passive Pressure Transducer for Implanting in the Eye", IEEE Transactions on Bio-Medical Engineering, Volume BME-14, pages 74-83, 1967. Collins' transducer used a hand wound inductor in a passive circuit. More recently, micromachining techniques have been used for similar LC passive circuits. Such systems achieve readout by using an absorption Q-meter
Pressure monitoring devices such as that mentioned above, have been applied to a number of medical applications and, in particular, to intra-cranial pressure measurement. The majority of such devices have been implanted with leads protruding from the cranial cavity. Micro engineering techniques applied to such devices enable drastic reduction in their dimensions and allow for easy implantation anywhere on the human body.
Resonant RLC devices have been reported, based on silicon technology, in which the capacitance varies with an external fluid static pressure. The resonant frequency of the RLC devices varies with static fluid pressure, as a capacitance diaphragm electrode spacing is varied. When any such device is implanted, it is desired that the device be externally powered and that its readout be available without requiring a direct connection to the implanted device. Further, the device should exhibit extremely small physical size to assure the least interference with other biological structures or functions. Remote power and readout pressure monitoring devices also have application in nonmedical areas including the measurement of pressure levels in untethered robotic equipment, automotive tires, systems with high vibration levels where electrical interconnections are not reliable, and in certain extreme miniaturization applications where interconnect wires are too massive.
Silicon microstructure technology provides a basis for the manufacture of high performance sensors at low cost and in high volume. In addition, silicon devices are typically small, rugged stable and unaffected by biological fluids. The basic silicon technology is identical to that employed in semiconductor devices and involves the patterning and chemical etching of wafers of silicon to create three dimensional structures. Recent process improvements enable very precise dimensional control and the achievement of multiple layers that are etched and then fused together to form highly complex three dimensional structures.
It is therefore an object of this invention to provide an integrated structure pressure sensor that is powered from an external source, without requiring direct electrical connection.
It is another object of this invention to provide an integrated structure pressure sensor wherein read out is accomplished without a requirement for a direct electrical connection.